What the Anesthesiologist Should Know before the Operative Procedure

Hydrocephalus is an abnormal enlargement of the cerebral ventricles. Causes of hydrocephalus include impaired elimination of cerebral spinal fluid (CSF), and less commonly, an increased production of CSF. Hydrocephalus may present in any age group with a wide variety of symptoms. Prior to the procedure, the anesthesiologist should establish the etiology of hydrocephalus and whether there is associated increased intracranial pressure (ICP).

In infants, intracranial hemorrhage and infection are two of the most likely causes of hydrocephalus. In developed countries, intraventricular hemorrhage of prematurity is among the leading causes of hydrocephalus. In contrast, ventriculitis is the primary cause of hydrocephalus in underdeveloped regions such as sub-Saharan Africa. Other causes of hydrocephalus in infants and children include trauma, infection, tumors, intracranial hemorrhage, vascular malformations, congenital abnormalities (e.g., aqueduct stenosis), Chiari II malformation, and myelomeningocele.

The most common type of surgery to treat hydrocephalus is the creation of a shunt from the ventricles to the peritoneal cavity (VP). Alternatively, CSF can be shunted to the atria or pleura. Shunts are composed of Silastic® tubing, are often tunneled subcutaneously, and consist of a ventricular catheter, a valve, and a distal catheter.

There are four types of valves that control the rate of CSF flow through the typical VP shunts. The standard valve is a differential pressure valve which utilizes the difference between intracranial pressure and peritoneal cavity pressure to drive CSF flow. In this type of valve, the higher the ICP, the greater the flow of CSF through the shunt. With the standard valve, excessive CSF drainage may occur when the patient is positioned with the head higher than the peritoneal cavity. This problem is addressed with the second type of valve, the anti-siphon valve, which attempts to prevent excessive CSF drainage.

Flow-regulated valves are the third variety of shunt valves. They drain CSF at a constant flow regardless of pressure. The fourth type is a programmable or adjustable shunt valve, which allows drainage based on a predetermined pressure. This pressure may be changed with an external device in a doctor's office or even the patient's home, without requiring reoperation or shunt replacement. The programmable shunt valve requires reprogramming if exposed to magnetic resonance imaging (MRI).

Patients with ventriculoperitoneal or ventriculoatrial shunts may present with shunt malfunction or infection, which can result in elevated intracranial pressure or meningitis. Shunts have a high degree of failure and frequently require revision or replacement.

When hydrocephalus is due to an obstruction of CSF flow at the level of the third ventricle, surgical treatment may consist of an endoscopic third ventriculostomy (ETV) with or without choroid plexus cauterization (CPC). This technique is performed in selected patients, providing a cure for hydrocephalus without the concern for shunt malfunction or infection. During the procedure, an endoscope is introduced into the lateral ventricle and passed through the foramen of Monroe and into the third ventricle, where a window is created, allowing CSF to drain directly from the third ventricle into the prepontine cistern.

The risk of ETV failure after initial placement is high among infants. The introduction of choroid plexus cauterization has improved the efficacy of ETV. With CPC, the entire choroid plexus of both lateral ventricles is cauterized, decreasing the amount of CSF produced. The outcome of ETV and CPC coupling in the treatment of hydrocephalus is under ongoing investigation.

Preoperative management 1. What is the urgency of the surgery? What is the risk of delay in order to obtain additional preoperative information?

If the patient has signs and symptoms of acute increased intracranial pressure, then this is a true surgical emergency. However, a large number of patients present with chronic symptoms, allowing time for a more complete evaluation prior to surgery.

Emergent

The patient is at risk for cerebral herniation with acutely elevated ICP. This presentation most commonly occurs with rapidly developing hydrocephalus or pre-existing shunt failure. Severe warning signs of elevated ICP include altered level of consciousness, seizures, bradycardia, apnea, and a Cheyne-Stokes pattern of breathing. In this situation, prompt airway protection by endotracheal intubation and maneuvers to lower ICP while preparing for surgery are indicated.

Temporarily reducing ICP can most easily be achieved by hyperventilation and elevation of the head if possible. Intravenous mannitol could be considered if herniation is impending and there is a delay in going to surgery. In patients with a pre-existing shunt, sterile tapping of the shunt with a small gauge needle to drain CSF may decrease pressure significantly. Patients requiring emergency surgery also frequently present with vomiting, and should be considered to have full stomachs, placing them at risk for aspiration.

Urgent

Patients in urgent need of surgical intervention show signs of shunt failure or increased ICP including headaches, alteration in level of consciousness, seizures, vomiting, and papilledema. Prompt surgical intervention is indicated but there is more time available to prepare the patient. These patients should also be considered to have full stomachs and are at risk of aspiration.

Elective

Patients presenting for elective treatment of hydrocephalus do not show acute signs of elevated ICP as seen in the emergent and urgent categories. Headache is one of the most common presenting symptoms. Infants and children may present with macrocephaly. Adults with normal pressure hydrocephalus (NPH) are typically in this category. Adults with NPH are usually elderly and typically present with gait changes, cognitive decline, and urinary incontinence. These vague symptoms are common in this population and diagnosis may be delayed. When patients present for elective hydrocephalus treatment, medical optimization should be performed prior to surgery.

2. Preoperative evaluation

The medical conditions affecting patients with hydrocephalus vary by patient age. Preoperatively, thorough histories and physical exams should be performed. All patients with pre-existing shunts should be evaluated for the presence of shunt infection. One should evaluate for seizures, which could be a new presenting sign or a chronic condition. In pediatric patients, sequelae of prematurity such as bronchopulmonary dysplasia, apnea, and bradycardia should be considered. In elderly patients, an assessment of comorbid conditions associated with aging, such as cardiovascular diseases, should be done.

Medically unstable conditions that warrant further evaluation prior to elective shunt surgery include unstable coronary syndromes. Ongoing seizures and status epilepticus should be medically treated prior to arrival in the operating room (OR), although it is possible that the seizures may continue until hydrocephalus is surgically managed.

Delaying surgery may be indicated if there is coagulopathy. Due to the serious complications associated with intracranial hemorrhage, coagulopathy should be addressed prior to arrival in the OR.

3. What are the implications of co-existing disease on perioperative care?

a. Cardiovascular system

Acute/unstable conditions

If the patient is suffering from active coronary conditions such as unstable coronary syndromes, decompensated heart failure, significant arrhythmias, and severe valvular disease, elective repair of hydrocephalus should be postponed (ACC/AHA guidelines 2014). However, if acute elevated intracranial pressure is the presenting complaint and there is an immediate threat to the patient's life, surgery must proceed. If the time allows, the following evaluation should be performed:

History and physical exam.

ECG with comparison to baseline.

Echocardiogram to evaluate for ventricular function, and for signs of ischemia and valvular dysfunction.

Chest X-ray to evaluate for cardiomegaly and signs of congestive heart failure.

Perioperative risk reduction strategies may include heart rate control to limit ischemia and judicious fluid therapy with close monitoring of volume status. If there are signs of ongoing ischemia, a cardiology consultation with possible coronary angiogram or coronary stenting may be necessary.

Pre-existing coronary artery disease or cardiac dysfunction

In adult patients with known cardiac disease undergoing elective noncardiac surgery and adherence to the American College of Cardiology/American Heart Association (ACC/AHA) guidelines on perioperative cardiovascular evaluation and management is recommended. Preoperative evaluation should include history and physical exam, with attention to exercise tolerance and angina. History of myocardial infarction, coronary interventions, coronary stents, heart failure, dysrhythmia, valvular disease, diabetes mellitus (DM), cerebrovascular accidents, and renal impairment should be elucidated. Current medical therapy including beta-blockade, antiplatelets, and anticoagulants should be assessed.

Further evaluation should be individualized by the patient's baseline cardiovascular risk according to the ACC/AHA guidelines, and may include EKG, stress test, echocardiogram, and nuclear imaging. Laboratory evaluation including CBC with platelets, coagulation studies, BUN/Cr, and electrolytes including calcium, magnesium, and phosphorous may be indicated. For patients with poor functional status and those with a prior history of coronary interventions or ongoing dual antiplatelet therapies, clear preoperative communication with the cardiologist is important.

According to the ACC/AHA guidelines, head and neck surgeries are considered intermediate risk, associated with less than 5% of cardiac risk. If there is anticipated prolonged duration of surgery or significant fluid shifts, then the surgery is considered high risk.

Perioperative risk reduction includes continuation beta-blockers in the perioperative period. For patients with high risk for cardiac morbidity, initiation of beta blockade at least one week prior to surgery may be considered. If there are any signs of worsening of baseline coronary artery disease or cardiac dysfunction, then perioperative consultation with a cardiologist should be considered prior to elective surgery.

Goals of management include prevention of tachycardia, maintenance of sinus rhythm, and maintenance of baseline blood pressure. In cases of congestive heart failure, avoidance of fluid overload is important.

b. Pulmonary

Chronic obstructive pulmonary disease

Patients with chronic obstructive pulmonary disease (COPD) undergoing surgery for hydrocephalus are at increased risk for postoperative pulmonary complications (PPC). Additional risk factors for PPC include age greater than 60 years, American Society of Anesthesiology status of 2 or greater, concomitant heart failure, and functional dependence. Preoperative evaluation should include history and physical exam with specific focus on exercise tolerance and recent exacerbations of disease. A thorough history should include tobacco use, oxygen therapy, obstructive sleep apnea, CPAP/BiPAP use, recent respiratory infections, and concomitant cardiovascular pathology. Assessment of functional status is important. Physical examinations should include the assessment of wheezing, prolonged expiratory phase, and work of breathing.

With the exception of assessment of an albumin level, which can be prognostic for PPC, diagnostic imaging and laboratory studies are not routinely indicated and should be used selectively. These studies include baseline spirometry studies, response to bronchodilators, and chest X-ray. An arterial blood gas to evaluate for carbon dioxide retention may be indicated in selected patients.

Reactive airway disease and asthma

Preoperative evaluation should include history and physical exam with a specific focus on history of steroid use, hospitalizations, intubations, and exposure to cigarette or cigar smoke. Assess for recent respiratory tract infections and asthma exacerbations. Laboratory evaluation may include baseline spirometry and response to bronchodilators.

Bronchopulmonary dysplasia

Preoperative evaluation should include history and physical exam with specific focus on degree of prematurity, history of intubation at birth, duration of intubation and ventilatory support, history of oxygen therapy and current oxygen need, NICU course and duration of NICU admission, and history of subglottic stenosis. If recent worsening of lung function is apparent on exam, further evaluation could include spirometry and bronchodilator response.

Perioperative risk reduction includes treatment of any active wheezing or exacerbation of symptoms if time allows, continuation of all pulmonary medications and oxygen therapy, possible preoperative bronchodilator use, and careful selection of endotracheal tube size to minimize risk of subglottic stenosis.

c. Renal

Chronic kidney disease and renal failure

In patients with acute renal failure, elective surgery should be postponed. Preoperative evaluation of patients with chronic kidney disease (CKD) includes history and physical exam with a specific focus on the disease severity, comorbid conditions, and underlying cause of kidney disease.

Assessment of baseline creatinine, history of urine production, history of dialysis, type of dialysis, last dialysis, access for dialysis, and examination of current volume status should be performed. The patient using peritoneal dialysis poses a specific challenge for VP shunt placement, so an alternative site for shunt placement should be considered. As DM is the leading cause of chronic kidney disease, glycemic control should be assessed. The presence of hypertension and antihypertensive therapy should be reviewed. Laboratory evaluation includes electrolytes, BUN, creatinine, hemoglobin, and coagulation studies.

Perioperative risk reduction includes careful volume administration to prevent volume overload, alteration of drug dosage for the degree of renal failure, avoidance of drugs that are metabolized by the kidney when possible, and maintenance of the patient's baseline blood pressure. Perioperative management of comorbid DM is discussed separately.

d. Gastrointestinal

From a gastrointestinal standpoint, preoperative evaluation includes the assessment for vomiting associated with neurologic symptoms, GERD, NPO status, and the presence of hepatic pathologies.

Patients presenting with a significant history of emesis or worsening emesis may raise concern for an acutely increased ICP. Additionally, they may be intravascularly depleted with electrolyte abnormalities, and may be at risk for aspiration. In the elective setting, patients with worsening symptoms should undergo imaging and medical evaluation prior to induction of anesthesia.

The evaluation of a patient with GERD should include symptom severity and current medical management. The pediatric patient with GERD and without intravenous (IV) access is a particular challenge. If the child is presenting for emergency surgery, intravenous access is required for rapid or modified rapid sequence induction for facilitation of prompt endotracheal tube placement. For elective surgeries in a pediatric patient with a history of GERD, the risk of upsetting the child and inducing vomiting by placing an IV line preoperatively must be weighed against that of an inhalational induction and IV placement after the child is asleep. In the elective setting, adherence to the standard ASA NPO guidelines is recommended.

In patients with acute liver failure, elective surgery should be deferred. In patients with chronic liver disease and cirrhosis, the decision to proceed with surgery should be made in conjunction with the patient's surgeon and hepatologist. Assessment of the patient's mental status, bilirubin, albumin, ascites, and INR is typically done to stratify the patient in Child-Pugh classes, a useful predictor of survival. Patients with chronic liver disease may have altered electrolytes, such as hypoglycemia, hyponatremia, and changes in mental status, which may worsen their neurologic states. Drug metabolism and clearance may be altered. The patient may be coagulopathic, with concurrent multi-systemic involvement such as pulmonary and renal disease. These patients must be medically optimized prior to elective surgery.

Perioperative risk reduction should include rapid or modified rapid sequence induction for patients requiring emergency surgery or significant GERD history. In patients with chronic liver disease, preoperative medical optimization should be performed.

e. Neurologic

All patients presenting for hydrocephalus surgery are known to have neurologic disease. Perioperatively, it is important to understand the patient's baseline neurologic function and how their presentation immediately prior to surgery compares to that baseline. History of seizures including frequency, type, and changes in seizure pattern is important. History of neurologic deficits, immobility, or paralysis is also important. Physical exam must include a basic neurologic exam. Laboratory evaluation includes antiepileptic medication levels, basic electrolytes with attention to the sodium level, and a urine toxicology screen if drug abuse is suspected. Imaging of the brain or of the existing shunt is often requested by the neurosurgeons and commonly includes a head CT scan or shunt series plain films.

Acute issues

Alterations in level of consciousness and seizures are the most serious of the acute issues. Perioperative risk reduction includes treatment of ongoing seizures with benzodiazepines or barbiturates and prompt surgical treatment of hydrocephalus to hopefully improve level of consciousness. As previously described, interventions to reduce ICP can be attempted while awaiting surgical intervention, including hyperventilation, head elevation, and the possible administration of mannitol.

Chronic disease

Baseline neurologic deficits should be examined and recorded prior to surgery. Perioperative risk reduction includes continuation of antiepileptic medications and avoidance of succinylcholine in patients with paralysis or prolonged immobility. When nondepolarizing muscle relaxants are used, nerve stimulation should be performed on the unaffected limb to avoid muscle relaxant overdose. Some anti-seizure medications induce the metabolism of nondepolarizing muscle relaxants, so careful monitoring of blockade is important.

f. Endocrine

Diabetes insipidus

Patients with a history of previous craniotomy may be at risk of neurogenic diabetes insipidus (DI) if there was damage to the pituitary gland. History of surgeries and any change in urinary habits should be evaluated. A patient with DI is at risk of becoming volume depleted without access to water as would occur during fasting for surgery or while under anesthesia. Laboratory evaluation should include electrolytes with specific concern for hypernatremia.

Perioperative risk reduction includes continuation of desmopressin (DDAVP) for treatment of DI, close monitoring of electrolytes, and placement of a bladder catheter to monitor urine output during surgery.

Diabetes mellitus

Patients with a history of either type 1 or type 2 diabetes are at increased risk of infection, hemodynamic lability, hyperglycemia, and hypoglycemia perioperatively. A careful history and physical exam should be performed with specific focus on type of diabetes, current treatment regimen, baseline blood sugars, hemoglobin A1c level, and any sign of infection. Adult patients with diabetes often have comorbid cardiovascular disease and renal disease, prompting a need for preoperative optimization.

Perioperative risk reduction includes continuation of the diabetes regime (with the exception of metformin which should be halted at least 24 hours prior to surgery), preoperative blood sugar measurement, close monitoring of intraoperative blood glucoses, and possible treatment with insulin. Diabetic patients often will have gastroparesis with increased risk for aspiration; for select patients, rapid sequence intubation with cricoid pressure may be prudent. In patients with concurrent cardiovascular disease, maintenance of baseline blood pressures, heart rate control, and vigilant monitoring for signs of cardiac ischemia is important.

4. What are the patient's medications and how should they be managed in the perioperative period?

The patient's medications should be reviewed prior to surgery. In the elective setting, the patient should be advised carefully on management of antiplatelet and anticoagulants. Please refer to specific recommendations as noted below.

a. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?

The patient's anti-seizure medications should be continued until the time of surgery. Timing of the last dose and the next scheduled dose should be elicited to ensure that there are as few gaps in anti-seizure medications as possible.

b. What should be recommended with regard to continuation of medications taken chronically?

Cardiac

Antihypertensive, rhythm controlling, and heart failure medications should be continued during the perioperative period. Beta-blockers should be continued perioperatively. Angiotensin-converting enzyme inhibitors (ACEIs) or angiotensin receptor blocking agents (ARBs) may cause significant hypotension while under anesthesia; these medications may be held 12-24 hours prior to surgery.

Pulmonary

All chronic medications to control COPD or asthma should be continued and preoperative bronchodilator therapy should be considered if there is wheezing on exam.

Renal

Diuretics should be discontinued on the day of surgery.

Neurologic

As previously discussed, anti-seizure medications should be continued until the time of surgery. Parkinson's and Alzheimer's medications may also be continued.

Hematologic

When stopping antiplatelet and anticoagulant medications, the risk of thrombosis must be weighed carefully against the risk of bleeding. Patients with a history of cardiac stents on antiplatelet therapy require special attention. As a general rule, elective surgery should be postponed until 4-6 weeks after placement of bare metal stents and 12 months after placement of drug eluting stents while on antiplatelet therapy. Antiplatelet medication management in patients with cardiac stents should be discussed with the patient's cardiologist and neurosurgeon.

In most patients, the risk of catastrophic bleeding during neurosurgery causing permanent neurologic deficits or death outweighs the risk of thrombosis, and most, if not all, antiplatelet and anticoagulant medications should be stopped prior to elective surgery.

Aspirin taken for primary prophylaxis should be discontinued 1 week prior to surgery. Other nonsteroidal anti-inflammatory drugs should be discontinued at least 2 days prior to surgery. If the patient has a cardiac stent, discuss with neurosurgery and cardiology.

Thienopyridines (e.g., clopidogrel and ticlopidine) should be discontinued 1 week prior to surgery. If the patient has a cardiac stent, discuss with neurosurgery and cardiology.

Warfarin should be discontinued and PT/INR followed until normalized. Vitamin K may be administered for reversal of INR in nonurgent situations and in patients where rapid postoperative anticoagulation is not immediately required. A heparin bridge may be required in patients with high risk of thrombosis. In the urgent setting where warfarin needs to be rapidly reversed, prothrombin complex concentrates or fresh frozen plasma can be given.

Psychiatric

Antidepressant, antipsychotic, and antianxiety medications may all be continued until the time of surgery with the exception of monoamine oxidase inhibitors, which should be discontinued for 2 weeks prior to surgery. A discussion with the patient's psychiatrist should take place before any psychiatric medication is discontinued.

c. Modify care for patients with known allergies

Every patient should be considered as at risk of developing an allergic reaction at any given time. Anesthetic environments should be equipped and anesthesiology staff prepared to manage allergic reactions. Epinephrine, steroids, and antihistamines should be immediately available.

d. Latex allergy

If the patient has a history of anaphylaxis or IgE-mediated allergy to latex, the operating room should be prepared with latex-free products.

Latex allergy is increasingly more common. Supplies should be readily available to avoid latex in sensitive patients. The most common latex-containing product are gloves. Both sterile and nonsterile latex-free gloves should be readily available. Other portions of the anesthetic environment that may contain latex are the anesthesia circuit bags and injection ports of intravenous lines and tubing. Anything that touches the patient should be examined for latex, including tourniquets, Foley, and implantable drains. For allergic patients, the operating room should be latex-free.

Children and adults with meningomyelocele are at increased risk for latex allergy and should be treated in a latex-free environment. These patients usually have shunts placed for control of hydrocephalus early in life and are frequently seen in the operating room for shunt revisions. For any given case, the operating room and anesthetic environment should have epinephrine, steroids, and antihistamines immediately available.

e. Does the patient have any antibiotic allergies?

Common antibiotic allergies and alternative antibiotics

For neurosurgical procedures, cefazolin is the most common antibiotic given prior to incision. For patients with beta-lactam allergies, vancomycin can be used.

f. Does the patient have a history of allergy to anesthesia?

Malignant hyperthermia

In patients with known malignant hyperthermia (MH), avoid all triggering agents such as succinylcholine and volatile anesthetics.

Proposed general anesthetic plan: Total intravenous anesthetic (TIVA) with a propofol infusion combined with an opioid infusion such as remifentanil. Remifentanil is uniquely advantageous for this procedure because it is easily titratable with an ultrashort half-life, allowing for prompt neurologic examination after the procedure. An infusion of dexmedetomidine can aid in anesthetic depth and hemodynamic stability. Nondepolarizing muscle relaxants can be used throughout the surgical procedure. Rocuronium, when appropriately dosed, achieves muscle relaxation nearly as fast as succinylcholine, facilitating timely endotracheal intubations.

Ensure MH cart is available: Adequate supplies of dantrolene (Dantrium, Ryanodex) should be easily available. Initiate the MH protocol when there is concern for the occurrence of MH. Call the free MH hotline (1-800) MH-HYPER for additional help in both diagnosis and management of a MH event.

Family history or risk factors for malignant hypertherma

A complete family history and a detailed history of the actual patient event are preferred. If elective surgery is planned, obtain the anesthetic record of the family member who suffered the MH event. Frequently, the event is not actually MH. In the absence of documentation however, a life-threatening event while under anesthesia should be treated as possible MH, and family members are considered MH susceptible.

Local anesthetic and muscle relaxant drug allergy

True local anesthetic allergies are uncommon and are frequently the result of misdiagnosis or an allergy to the preservatives contained within the local anesthetic solution. Amide local anesthetics, such as bupivacaine and ropivacaine, are less likely to cause an allergic reaction compared to ester local anesthetics such as tetracaine and chloroprocaine. With ester-type local anesthetics, a common metabolite is closely related to para-aminobenzoic acid (PABA), a compound that can cause allergic reactions in some individuals. Both ester and amide local anesthetics may be commercially prepared in solutions containing methylparaben or chemical relatives of PABA, substances that can be allergenic. Preservative-free preparations are available. Alternatively, local anesthetics may be avoided if the patient has a documented allergy.

Muscle relaxants are the most commonly used allergens during an anesthetic and an allergic reaction may occur at any time during their use. Sensitization may occur with prior drug exposure, though it may also occur with over-the-counter medications and cosmetics. Cross-sensitivity between muscle relaxant drugs may occur. In patients with a known allergy, referral to an allergist/immunologist for skin testing can be helpful to determine if there are non-allergenic muscle relaxant alternatives. In some patients, muscle relaxants may need to be avoided entirely. As with the delivery of any anesthetic, epinephrine, steroids, and antihistamines must be immediately available.

5. What laboratory tests should be obtained and has everything been reviewed?

Laboratory tests and imaging prior to hydrocephalus procedures should be individualized to the patient. Generally, the greatest concern is for complications associated with bleeding; it is therefore customary that a complete blood count (CBC with platelets) and coagulation panel (PT, PTT, INR) be obtained preoperatively. Typically, excessive bleeding does not occur during the procedure unless the patient is coagulopathic. Other laboratory evaluations can be tailored to the patient (e.g., electrolytes in a patient presenting with vomiting).

In the premature infant, even seemingly minor bleeding may represent a significant portion of the entire blood volume. In these patients, obtaining a baseline hemoglobin and coagulation panel is of particular importance; a type and screen should be considered. Any patient with a coagulation disorder that cannot be reversed prior to surgery should have a type and screen. Type and cross with blood available prior to surgery in an anemic patient would be prudent.

Hemoglobin levels

Obtaining a baseline hemoglobin level is important to allow for the calculation of maximum allowable blood loss, particularly for the pediatric patient. Most patients will not require preoperative blood transfusion if the hemoglobin is greater than 10 g/dl, although a premature or newborn infant may require transfusion at this level.

Electrolytes

In patients presenting with nausea and vomiting, there is concern for hyponatremia, hypokalemia, hypochloremia, and metabolic alkalosis. If these are present, appropriate hydration should be given and electrolytes monitored during the surgical procedure. Glucose levels should also be checked and a dextrose containing solution be given if necessary as hypoglycemia may be difficult to detect while under anesthesia and may manifest as a change in mental status while awake.

Platelets and coagulation

Platelet counts should ideally be greater than 100,000/microliter prior to surgery. Assessment of platelet function should be considered in patients who take platelet inhibitors such as clopidogrel. If there is either a low platelet count or recent platelet inhibitor therapy, timing of surgery should be discussed with the surgeon. If platelet count is low, elective surgery should be postponed until the count is greater than 100,000/microliter. Platelets should be available prior to surgery.

INR should be near normal at less than or equal to 1.4 prior to the procedure. In the setting of an abnormal INR, fresh frozen plasma should be available. Depending on the urgency of surgery, correction may take place in the operating room or prior to surgery with documentation of INR less than 1.4 prior to incision.

Imaging

In patients with pre-existing ventricular shunts, shunt series X-rays can be obtained to assess the entire length of the shunt or catheter for any visible damage or breaks. Head CTs are often done, and should be reviewed prior to surgery, with particular attention paid to the presence of hydrocephalus, signs of midline shift, or cerebral herniation.

For elective cases, MRIs may assist in both diagnosis and surgical planning without the risk of exposure to radiation. Minimization of radiation is of particular importance in the care of the pediatric patient. In elective situations, other studies can be performed based on a patient's underlying comorbidities; these include EKG, chest X-ray, echocardiogram, and cardiac stress tests.

Intraoperative Management

1. What is the author's preferred method of anesthesia technique and why?

What are the options for anesthetic management and how to determine the best technique?

Most hydrocephalus procedures involve a general anesthetic. One exception is the case of placement of an external ventricular drain, which could be performed under local anesthesia or with minimal sedation.

Regional anesthesia

Regional anesthesia is not an option for hydrocephalus procedures.

General anesthesia

Benefits

General anesthesia allows for control of patient movement and hemodynamics. Multiple different regimens of general anesthesia can be utilized, including pure volatile anesthetics, a combination of intravenous agents, and volatile agents combined with opioid techniques. Muscle relaxants may be utilized and are especially useful in patients who do not tolerate volatile anesthetics alone.

Drawbacks

Use of greater than one MAC of volatile anesthetic may increase cerebral blood flow, leading to increased ICP, which may put the emergent or urgent surgical patient at risk of cerebral herniation. A balanced anesthetic combining volatile agents, opioids, and muscle relaxants may provide optimal conditions.

Other issues

Typically, the patient is in the supine position with the table turned 90 degrees away from the anesthesiologist. This position allows for easy surgical access to the patient's head. The arm farthest from the anesthesiologist is often tucked and not available for immediate access during the surgical procedure. Proper padding and positioning are essential prior to draping. Temperature regulation may be difficult because the head is only partially covered with a drape while the chest and abdomen are exposed. Warming devices can be placed on the patient's legs. Ideally, an underbody should be placed, particularly for the pediatric patient whose body temperature may drop rapidly.

Airway concerns

Definitive airway management with endotracheal intubation is the most commonly utilized approach for hydrocephalus procedures. Emergent surgical patients should be treated as having full stomachs and rapid sequence induction should be considered. It is possible to perform the procedure with a laryngeal mask airway (LMA), however this is not ideal due to lack of access to the patient's head and airway during the procedure; furthermore, possible movement of the patient's head during surgical manipulation may alter the LMA's position.

Monitored anesthesia care

Benefits

In the medically unstable patient at significant risk with general anesthesia, an extraventricular drain (EVD) can be placed with local anesthetics alone or in combination with sedation. In some situations involving critically ill patients, EVDs are placed in the intensive care unit without the anesthesiologist's involvement. In addition to minimizing hemodynamic fluctuations associated with general anesthesia, a major benefit of performing the procedure with the patient awake or mildly sedated is the ability to assess immediate postoperative neurologic status. Sedation and local anesthetics would likely be inadequate if the procedure involves a shunt, as it requires tunneling of the shunt catheter from the head to the abdomen.

Drawbacks

Placing an EVD requires making a burr hole through the skull, which can be highly uncomfortable for the patient under sedation. Pain can be minimized if a local anesthetic is appropriately administered. A cooperative or severely neurologically impaired patient is required for this to be successful. Placement of an EVD in most pediatric patients using sedation alone is very difficult, if not impossible.

Other issues

As with any other procedure, if EVD placement is performed at a remote site away from the operating room, appropriate equipment, medications, and staff must be present. During the procedure, close monitoring is needed, and in the event of patient oversedation or neurologic decompensation, airway instrumentation may be needed promptly.

2. What prophylactic antibiotics should be administered?

Cefazolin can generally be used unless there is beta-lactam antibiotic allergy or specific infection. In allergic patients, vancomycin or clindamycin may be used. In the case of known infections, individualized antibiotic therapy targeting specific pathogens should be used.

3. What do I need to know about the surgical technique to optimize my anesthetic care?

Shunts typically require an incision in the scalp, creation of a small burr hole through the cranium, placement of the ventricular catheter, implantation of the one-way valve under the scalp, and tunneling of the catheter to a distal site. The surgical field is often prepared from head to abdomen. After scalp incision and creation of a burr hole, a catheter is advanced into the ventricle. The valve, which allows CSF to flow in the direction of the distal catheter and prevents retrograde flow into the ventricles, is placed into a subgaleal pocket, often created posterior to the ear.

The distal end of the shunt may be tunneled under the skin to the desired location. There are several possible locations for placement of the distal portion of the ventricular shunt. These include the peritoneum, the atrium, and the pleura. The most common type is the peritoneal shunt. Other surgical services may be present to facilitate placement of the distal catheter tip including general surgeons to access the peritoneum, or thoracic surgeons to access the pleura. If a ventriculoatrial shunt is planned, access is typically gained via the internal jugular vein.

Not all patients with hydrocephalus require a shunt. Endoscopic third ventriculostomy (ETV) is primarily used for patients with an obstruction to the distal or posterior third ventricle. An endoscope is used to create a hole in the floor of the third ventricle, bypassing the obstruction. This technique is commonly utilized in pediatric patients. Anesthetic management is similar to that for shunt placement: general anesthesia with endotracheal intubation and careful regard for ICP. Muscle relaxation is often beneficial for surgery as patient movement during brain endoscopy can lead to significant injury.

4. What can I do intraoperatively to assist the surgeon and optimize patient care?

The most stimulating part of the procedure is the tunneling of the distal catheter. Temporarily increasing the anesthetic depth by giving a bolus short-acting opioid and/or muscle relaxant may improve patient comfort and provide optimal surgical conditions.

5. What are the most common intraoperative complications and how can they be avoided/treated?

Complications may occur at any time during the placement of the catheter and shunt. Hypotension may occur during access to the lateral ventricle. If the ventricular drain is not placed appropriately or excessive bleeding occurs, an increase in ICP may result, with possible herniation. Warning signs include bradycardia and hypertension. During tunneling of the distal catheter, injury to any of the structures along the path of the catheter is possible, including parts of the neck, such as the great vessels and the trachea; chest wall injury and development of pneumothorax may occur.

If the catheter is placed in the atrium, potential complications include dysrhythmia and venous air embolism. If possible during venous access, the patient should be placed in the head down position, although during placement of the ventricular drain the patient is usually slightly head up. Peritoneal catheters may injure the liver when placed on the right side and may injure the spleen and stomach when placed on the left side. A careful surgical technique can avoid most of these injuries while vigilant monitoring of the patient may detect these complications early.

ETV may be complicated by significant bleeding; basilar artery injury can lead to catastrophic results. During fenestration of the floor of the third ventricle, significant bradycardia and even asystole can occur; in these instances, the surgeon must be notified immediately. Other complications of ETV include CSF leak, meningitis, hypothalamic injury, and cranial nerve injury.

Complications

Cardiac

If an atrial shunt is planned, rhythm disturbances may occur and may indicate the need for repositioning. Venous air embolism is possible during access of internal jugular vein or catheter placement.

Pulmonary

Pneumothorax may occur during placement of ventriculopleural shunt, during tunneling of a peritoneal shunt, or during placement of an atrial shunt.

Neurologic

Significant intracranial bleeding with resultant increases in ICP and cerebral herniation is possible. If endoscopic third ventriculostomy is performed, it can be difficult to accurately judge the amount of bleeding; this knowledge is important in the management of all patients, and is of critical importance in the management of young infants. All patients undergoing ETV are at risk of basilar artery injury and resultant bleeding.

6. If the patient is intubated, are there any special criteria for extubation?

The patient's neurologic status and ability to protect the airway at the end of the procedure are the most important factors in determining if it is safe to extubate. Extubation while the patient is under a deep plane of anesthesia is not advised. In adult patients, the ability to follow commands should be determined. Both adult and pediatric patients should be assessed for cough and gag reflexes. As with any surgical patient, prior to extubation of a patient after hydrocephalus procedures, one should evaluate for appropriate respiratory rate, adequate tidal volumes, minimal need for oxygen support, stable hemodynamics without significant vasopressor support, and adequate reversal of neuromuscular blockade.

Postoperative Management

1. What analgesic modalities can I implement?

Surgeries for hydrocephalus are invasive and patients will require careful pain management postoperatively. The combination of opioids, acetaminophen, and local anesthetic infiltration at the surgical sites provides excellent pain relief. Nonsteroidal anti-inflammatory drugs should be avoided until approved by the neurosurgeons given the risk of bleeding. Ketamine should be avoided because of potential interference with the neurologic exam and the associated increase in ICP.

2. What level bed acuity is appropriate?

Depending upon the urgency of the surgery and the status of the patient, different levels of monitoring may be appropriate after surgery. Judgement with regards to postoperative disposition should follow general standards based on the patient's condition and the nursing and monitoring capacity of the inpatient floors. In the stable patient with an electively placed shunt for NPH or macrocephaly, admission to the regular inpatient floor may be possible. For patients with active infections, sepsis, elevated ICP, or those who require vasopressor therapy, admission to the intensive care unit would be prudent. There should be clear communication among the anesthesiologist, the neurosurgeon and the receiving medical team regarding patient transfer.

3. What are the common complications, and ways to prevent and treat them?

Shunts have a high rate of failure. In pediatric patients, shunt failure is up to 40% in the first two years after placement. Reoperation is commonly required. Infection occurs at a rate of 8% to 10%, especially early after placement.

It is possible for the shunt to excessively drain CSF, resulting in positional headaches that are worse in the upright position with improvement in the supine position. This condition can be treated by reprogramming the shunt. If a reprogrammable shunt was placed, an external device can be placed over the one-way valve on the scalp for reprogramming. If the shunt is not reprogrammable, additional surgery may be required.

ETV failure occurs in up to 35% of patients, with highest rates among infants. Failures typically occur early, in the first six months after surgery. Infection rates are relatively less compared to shunt placement - about 2% compared to 10%.

Less common complications include bowel injury and excessive bleeding resulting in neurologic catastrophe. Other complications include hypothalamic injury and endocrinopathy. Patients undergoing hydrocephalus procedures have a perioperative mortality risk of 0.2-0.5%. Other complications include postoperative delirium, deep venous thrombosis and pulmonary embolus, reoperation for bleeding, and functional decline.

The type of shunt placed does not affect failure rate. Additionally, in the pediatric patient, shunt and ETV placement have similar efficacy and equivalent outcomes.

What laboratory tests should be obtained and has everything been reviewed?